Yesterday I was watching Discovery’s Project Earth, avoiding doing homework and grading. It’s an interesting show, with ideas ranging from the interesting to the preposterous. The episode I saw proposed launching little lenses into space to scatter a small fraction of the sun’s light away from earth. The tests were failures, and more damning but glossed over in the program were the sheer number of launches needed to put a significant number of lenses in space. At that point, why not just use reflective mylar sheets in space? They’re much cheaper and you can put a lot more in space with each launch. Or what about just installing mirrors on the earth’s surface? That’s probably not practical due to the absorbing effects of the atmosphere before the light gets to the surface, but this is getting pretty far out of my area of expertise as it is.

The next episode tested microwave power from space. This idea I’m a big fan of. Practical? Not yet. But none of the technology is beyond reach and it doesn’t require impossible expenses before seeing any perceptible benefit. Once the first satellite goes up it will start producing return on investment. The energy is clean, reliable, perfectly safe, and effectively limitless. It’s just not affordable or efficient enough yet. I’m hopeful that it will be soon.

Pet peeve: multiple times the show has described some physical process (say, diminution of light with distance) as “exponential”. No you idiots, it’s quadratic. But you can’t have everything.

Anyway, the reason I started writing this post is to note that there was a commercial break which included an ad for Sharp TVs. “Seems like you need to be a physics professor to choose the right TV,” the man on screen said. “Luckily, I am one”. Well, it’s a little silly but it’s good to see us getting some exposure even if it is just the “generic oracle of smartness” stereotype.

Weekend reading:

First, two posts from Carl Brannen. Here’s one which is non-physics examination of the better mousetrap. Here’s another, discussing relativity. Normally it’s quantum mechanics which is famous for having dozens of interpretations each trying to describe what “really” happening behind the mathematics. It’s lesser known that to some extent that relativity also has some interpretation issues – in particular, the possibility that it actually is compatible with a preferred reference frame, just one that isn’t detectable. It’s sort of fringe, but there’s nothing wrong with playing around in the fringe so long as it’s mathematically sound and willing to defer to experiment.

Here’s Swans on Tea, noting that the LHC is just the latest in a long list of experiments and phenomena that were supposed to kill us but didn’t. Well, to be perfectly honest the collisions that were supposed to kill us haven’t actually happened yet. But they won’t kill us. They will be awesome, and tell us all kinds of thing about the world.

Here’s Talk Like a Physicist on CERN tattoos. Hey, I like physics too, but not that much.

How’d the hurricane go? I don’t know, I’m typing this the night before in case the power goes out. Assuming the electricity keeps flowing and the internet stays functional I’ll update later today to give an inland Texas perspective on the hurricane.

Have a great weekend everyone!

Update: The power stayed on. It’s been very, very windy and the rain is torrential. But aside from tree branches and some slight debris strewn about, things seem to be fine. Looks like the actual hurricane impact zone was less badly hit than feared, as the storm surge fortunately did not match the models. But it’s always better to be safe and get out. In this case I’m sure it’s still bad enough that those who didn’t will wish they had.

The only obvious risk from transmitting large amounts of energy back to earth by microwave would be if the energy density was high enough in some locations to affect birds for aircraft flight paths, particularly if the satellite is not in a geosync orbit (as it likely can’t be because that area is already getting filled up with comm sats).

But we are already collecting solar energy and transmitting it to earth: it is called Direct TV.

I was amused that someone thought they could play a football game on Monday. With what electricity, water, lodging, and transport system for the fans?

I hope the surge was not as bad as it might be up in the TX/LA border area that did not have the local news coverage.

My comment to you is that there will be a major impact on TAMU. You will have (a) students mobilized out of class for NG service, perhaps for a week or more, and (b) students totally distracted by family affected in the Houston and E Tx area, perhaps for weeks.

The microwave broadcast schemes I’ve seen involve power densities that are similar to those in sunlight (with conversion efficiencies of 90% or higher, they would provide much more electricity than a photoelectric farm of the same size without interdicting the ground). They’re intended to be safe for birds and airplanes. The receivers, built as big metal antenna farms 3 metres off the ground would not block much sunlight, and could still be used for pasturage. One problem with running these satellites in a lower orbit than geosynchronous is that you get a lower duty cycle and, at very low altitudes, significant air drag on what is, by design, an object with a high area to mass ratio.

If the satellite doesn’t have a receiver farm in sight, the sunlight hitting it is not tapped, which means you’re not getting as much electricity back for the cost of launching your hardware, which makes low orbits less desirable. If your design can operate across 36000 km, though, a non-equatorial geosynchronous orbit is probably fine for a solar power satellite. You don’t need a stationary orbit, because the receiving array doesn’t tilt to follow the satellite, it tracks the satellite by phase shifting. There’s still a lot of room in the non-equatorial slots, though those ones do cross the stationary band, you can fit a lot of them up there.

I understand that there is a popular computer game where solar power satellites occasionally fire death rays into your cities because they get mispointed. This isn’t a realistic danger. The way you design a microwave power system is that the ground station sends up a low energy microwave beam from its compound antenna array. This beam is phase-tuned to deliver the energy on the satellite’s transmitter array, which then phase-inverts the signal it receives, boosts the power, and fires it straight back the other way. It doesn’t have the hardware or software to fire a beam at anything, all it can do is ride a pilot beam backwards to its source. And, because of the wavelengths involved, it can’t pump energy back down a pilot beam that hasn’t been made by a large phased array. So, nobody is going to redirect that beam unless they can surreptitiously build a few square kilometres of antenna and hook it up to a microwave generator.